Prostate cancer is one of the most commonly diagnosed cancers in men. Currently, the most accurate diagnosis of prostate cancer is determined using the Gleason grading system of analyzing stained prostate biopsies. The Gleason grading system was developed in the 1960s by Donald Gleason, a pathologist at the Veterans Administration, and was modified and improved in 2005 by the International Society of Urological Pathology. The Gleason grading system indicates the severity of the prostate cancer by correlating patterns in prostate biopsy specimens with tumor mortality rates. The Gleason method evaluates the glandular architecture of the prostate tissue based on the relative sizes of separate prostate glands and the regularity of the overall pattern of the glands. Tissue in which some glands are large and neighboring glands are small is graded as being more malignant and results in a worse prognosis. In addition, glands arranged in a disorganized, irregular pattern with only a small area of stroma between the glands are graded as being more malignant.
Cancerous prostate tissue is classified into five grades 1 through 5 of decreasing regularity. The grades of the two patterns that cover the largest areas of the biopsy tissue are added to obtain the Gleason score. The primary Gleason grade must be greater than 50% of the total pattern of the cancerous tissue. The secondary Gleason grade must be less than 50%, but at least 5%, of the pattern of the total cancer observed. If the secondary pattern covers less than 5% of the total area of observed cancer, the secondary grade is assigned the same grade as the primary grade. The sum of the primary and secondary Gleason grades is the Gleason score. For example, if the most prevalent pattern falls within grade 4 and the second most prevalent pattern falls within grade 3, then the Gleason score is 7.
Gleason grading is typically performed by a pathologist who visually evaluates a magnified image of a stained tissue sample. The pathologist manually inspects each cancerous area of a slide of stained tissue, classifies the patterns of the glands in each area based on the regularity and arrangement of the glands, and assigns a Gleason grade to each area of the tissue being graded. Then the pathologist determines the overall Gleason score for the tissue sample based on which Gleason grade was assigned to the largest area and to the second largest area of the tissue.
Manually grading prostatic tissue is difficult because the pathologist must evaluate a large number of cancerous areas consistently over a highly magnified image of stained tissue. The pathologist may not miss any cancerous areas. Moreover, the pathologist must consistently evaluate the gland patterns in the various areas of the tissue slide and other tissue slides in order to obtain an accurate Gleason score.
A method is sought for improving the prognostic accuracy of grading performed on stained prostate tissue by reducing the inconsistencies and missed areas that commonly occur with manual Gleason grading.